Hyomental Distance Ratio and Difficult Laryngoscopy

The patient is lying supine on a horizontal, flat bed.

The neutral position is with line of site perpendicular to the exam table surface.

The position of maximal head extension without elevating the shoulders from the exam table suface.

The hypomental distance (from hyoid bone to chin) and thyromental distance are measured in each position.

hyomental distance ratio =

= (hyomental distance in cm with maximal head extension) / (hyomental distance in cm in the neutral position)

Predictors of difficult laryngoscopy:

(1) hyomental distance ratio <= 1.2 (AUC 0.78)

(2) hyomental distance at maximal head extension <= 5.3 cm (AUC 0.64)

(3) thryomental distance at maximal head extension <= 6.2 cm (AUC 0.66)